Keep declared methods of generic class instances after a computed-key write - #1215

… write

When a write with a computed string key can replace any method, calls of
every method name read the receiver's property bag without checking for
the key, and the bag falls back to the class's prototype data. Generic
class instantiations, mixin classes and their subclasses have no prototype
data, so their methods read as undefined and calls threw "x.status is not
a function". Reads on these classes now check for an own property and
otherwise use the declared method.

Fixes #963
Co-authored-by: Quim T. <[email protected]>

…write

observedPrototypeMethod skipped classPrototypeData for function-local
classes, which also marks such a class as needing prototype data, so its
instances got no prototype behind their property bag. A function-local
class value's prototype holds only methods the program replaced there, so
reads of a marked method name on its instances now check for the
property, own or inherited, and otherwise use the declared method, as for
generic class instances. The prototype data is built again, so a method
replaced on the class's prototype stays visible.